1. Field of the Invention
This invention relates to an improved method for the concentration of a liquid-solid slurry containing a solid particulate component. More particularly, it relates to a novel method for the concentration of a slurry comprising a crystalline organic compound and the mother liquor resulting from the crystallization of the compound, especially for the concentration of a p-xylene slurry.
2. Prior Art
The separation of a solid from a slurry of the solid in a carrier liquid is an ordinary operation in the art, for example by filtration, centrifugation, sedimentation, and the like. Usually the equipment employed represents a substantial investment. An objective of the present invention is to reduce the burden on such equipment or the time required by removing a substantial portion of the carrier liquid prior to the final filtration, centrifugation or sedimentation.
The art relating to p-xylene recovery methods has advanced greatly. Larger crystals of p-xylene can now be grown rapidly. The need for an even-purer product has in large part been met. Most process operations have been made more efficient. However, there is yet a substantial room for improvement in certain areas. For example, in the concentration of a p-xylene slurry, blinding and icing of the filter screen is a serious disadvantage. This recurring problem is usually handled by use of a backwash employing a warmed filtrate, by use of mechanical scraping or by a combination of these expedients. By the employment of an in-line filter and a turbulently flowing slurry, longer intervals between the screen-clearing operations have been achieved. But filter-screen plugging and clearance, between the filter screen and stationary parts such as blades or brushes, disrupts the continuity of the processing and is frequently a serious bottleneck for what otherwise could be a continuous process. See, for example, U.S. Pat. Nos. 2,800,411 (use of brushes or backwashing to dislodge filter cake); 2,820,070 (stationary filter); 2,848,519 (stationary filter); 3,177,265 (use of backwashing to dislodge filter cake and conventional centrifuge separators) and 3,477,575 (continuous filtration process in which crystal cake is removed from a rotating filter element by the intensive agitation action generated between the rotating filter element and stationary filter elements or blades).